1. Field of the Invention:
The present invention relates to a motorcycle, and more particularly to a motorcycle having no body frame and including a front swing arm supporting a front wheel on a front end thereof and a rear swing arm supporting a rear wheel on a rear end thereof, the rear and front ends of the front and rear swing arms being pivotally mounted on an engine unit mounted centrally on the motorcycle.
2. Description of the Relevant Art:
Most of conventional motorcycles in general use employ so-called body frames.
There have been proposed in recent years frameless motorcycles including a front swing arm supporting a front wheel on a front end thereof and a rear swing arm supporting a rear wheel on a rear end thereof, the rear and front ends of the front and rear swing arms being pivotally mounted on an engine unit mounted centrally on the motorcycle. One such frameless motorcycle is disclosed in U.S. Pat. No. 4,265,329 issued May 5, 1981.
In the disclosed frameless motorcycle, front and rear plates are fixed to the front and rear ends of an engine unit disposed centrally on the motorcycle, and front and rear swing arms are vertically swingably attached to the front and rear plates, respectively. A steering plate is disposed on the front end of the front swing arm, and a rear wheel is rotatably supported on the rear end of the rear swing arm.
Since the motorcylcle disclosed in the above U.S. patent does not have any frame and front fork, it is lighter and has a lower center of gravity than motorcycles employing frames.
For servicing engine cylinders on such frameless motorcycles, it is preferable to remove the front and rear swing arms from the engine unit. It is however quite time-consuming to detach the front and rear plates from the engine unit because these plates are securely fixed to the engine unit. Therefore, a time-consuming and complex procedure is required to service the engine cylinders. Particularly, a front engine cylinder adjacent to the front swing arm near a steering mechanism cannot be serviced with ease. This problem manifests itself especially when a recently developed V-shaped engine having front and rear engine cylinders is to be serviced. It is suggested in the above U.S. patent that the plates may be replaced with protuberances integrally molded with the engine unit itself. With such an alternative, the front and rear swing arms are coupled to many protuberances on the engine unit. It would be more time-comsuming to detach the arms from the engine unit than to detach the arm together with the plates.
Another problem with the disclosed frameless motorcyle is that in the absence of a frame, particularly a main frame, a complicated structure is required to support a steering post and an air cleaner element.
Inasmuch as no main frame is used, a member which supports a rider's seat is attached to the engine unit. As a result, the structure around the engine unit is complex, preventing the engine unit from being serviced efficiently. The number of parts used is large. A portion of the engine unit to which the rider's seat supporting member is attached is required to be of an increased thickness, with the result that the engine unit itself, and hence the entire motorcycle are heavy.
The present invention has been made in an effort to solve the aforesaid drawbacks of conventional frameless motorcyles.